Prior art electronic marker devices are known which have a tuned circuit that is sealed within a plastic envelope. The tuned circuit is made up of a circularly wound coil of wire connected in parallel with a capacitor, with the assembly having a generally toroidal configuration. The plastic envelope has a generally "U"-shaped periphery with the side at the top of the "U" being initially opened and being sealed after the tuned circuit assembly has been inserted.
Another electronic marker device is disclosed in U.S. Pat. No. 4,334,227 to Barry M. Marks which is hoop shaped and includes a mandrel on which the coil for a tuned circuit is wound with a cover band provided to cover the coil. The mandrel has a thin, central web with a center opening in the web which is used for mounting the mandrel to a spindel to facilitate winding of the coil on the mandrel during manufacture of the device.
None of the prior art devices is constructed so it can, if desired, be readily secured to a strip of flexible material for burial with the marker or secured to a flat surface, such as the ceiling of a buried utility vault.